Auto High Beam (AHB) systems and alternate systems for controlling the light beam illumination in front of a motor vehicle have become desired features in vehicles and generally function to maximize the use of high beams at night by identifying oncoming and preceding vehicles and automatically controlling the high beam lighting pattern. Prior systems are known for controlling exterior vehicle lights in response to images captured forward of the vehicle by an imager such as a camera. In some instances, the imager's field of view may become blocked by obstructions such as snow, fog, dirt, frost, or condensation. Thus, for these systems to be effective, it is crucial to be able to identify when an imager becomes blocked and quickly remedy the situation. While some prior systems may already employ methods for identifying and eliminating a blocked imager condition, it is desired to provide an additional method for detecting a blocked imager condition, which may be used to supplement, or in place of, existing methods.